Oil cracking and hydrotreating process



June 6, 1961 M. c. CHERVENAK 2,987,468

OIL CRACKING AND HYDROTREATING PROCESS Filed Dec. 12, 1958 qAs BLOWER 27 FIG.1

26 OIL-CLAY SLURRY 21 25 2 2 TREATED Hz CLAY A 1o. 11 Ian; o||

42 r PREHEATER 24 T L RECYCLE 16 l5 TREATED G OIL X 60 52 CATALYTIC HYDROTREAT- 40 ING SECTION HYDROCRACKED SECTION42 k 51 PUMP 8 I I H; CLAY A 44 45 OIL K 4 j INVENTOR.

* HEATER MICHAEL C. CHERVENAK AGENT United States Patent 2,987,468 OIL CRACKING AND HYDROTREATING PROCESS Michael 'C. Chervenak, Pennington, N J., assignor to Hydrocarbon Research, Inc., New York, N.Y., a corporation of New Jersey Filed Dec. 12, 1958, Ser. No. 780,023 8 Claims. (Cl. 208-99) This invention relates to an improved process of treating hydrocarbon oils with hydrogen in the presence of a catalyst. More particularly, the invention is concerned with the catalytic treatment of heavy hydrocarbon oils to etfect hydrocracking and hydrodesulfurization.

It has been disclosed in copending application Serial No. 737,711, filed May 26, 1958, that the catalytic hydrotreatment of a heavy hydrocarbon oil is advantageously ifected when the oil is first precracked in the liquid phase in the presence of hydrogen or a comminuted contact material, or both. As shown in the copending application, the precracking step results in a reduced requirement for catalyst regeneration and replacement in the subsequent step by removing oil-soluble metalloorganic impurities which tend to inactivate the catalyst, or by rendering such impurities insoluble in which form they'have little effect on the catalyst. It was also found that the precracking step aids in the elimination of very refractory sulfur-containing compounds, e.g., heterocyclic sulfur compounds frequently present in heavy oils. The heavy oils which this prior process is designed to treat ordinarily contain at least 10% by volume of hydrocarbons which boil above 900 F., and the liquid phase precracking step is carried out so that at least 25% by volume of these components boiling above 900 F. are cracked to hydrocarbons boiling not in excess of 900 F. The efiluent from the precracking zone is then subjected to a hydrotreatment in the presence of a hydrogenation catalyst. Both steps of this prior process may be carried out by various techniques as disclosed in application Serial No. 737,711 and discussed hereinafter.

While the process disclosed in the aforesaid application when carried out as described therein is very effective in achieving the catalytic hydrotreatment of heavy oils with a minimum of catalyst regeneration and replacement, it has been found that there are some difliculties in its operation. These operational difiiculties are connected with the fact that the liquid in the cracking zone tends to have a low gravity, e.g., to 5 API, and also tends to be very unstable due to the fact that it contains a substantial amount of olefinic components and a relatively high carbon-to-hydrogen ratio. These tendencies lead to the troublesome deposition of impurities, e.g., coke, tars, gums, asphaltenes, etc., on the equipment and/or catalyst. The instability of the oil in the cracking zone results from one or both of two factors: the charge stock itself may be relatively heavy and unstable and conditions in the cracking zone may result in the substantial formation of olefins and unstable components. Even if the charge stock is relatively stable, the liquid remaining after the cracking treatment is generally heavier and less stable. The deposition of solid or semi-solid impurities causes the process to be less efficient and may ultimately result in its interruption.

It is an object of this invention to provide an improved process of catalytically hydrotreating heavy hydrocarbon oils to eliminate sulfur and produce lighter hydrocarbons whereby the regeneration and replacement of the catalyst is minimized. A further object is to hydrotreat heavy hydrocarbon oils efiiciently in the presence of a catalyst, using a precracking step in accordance with the-disclosure of application Serial No. 737,711, while avoiding or suppressing the deposition of impurities.

These objects are accomplished by recycling at least a portion of the liquid effluent from the catalytic hydrotreating or hydrodesulfurization zone to the cracking zone. It has been found that even a small stream of the relatively stable liquid from the catalytic hydrotreating second zone when added to the liquid passed through the cracking first zone results in a substantial stabilization of the liquid in the cracking zone and curtailment of impurity deposition.

Various techniques for carrying out the precracking and catalytic hydrodesulfurization steps may be used as illustrated in application Serial No. 737,711. For example, in the precracking step, the liquid oil together with hydrogen and/or contact material may be sent through a cracking coil of appropriate length at the desired temperature and pressure. Another method of precracking is to pass the oil upwardly through a relatively coarse mass of particulate solids in a cracking zone at a rate suflicient to cause the particulate solids to be in random motion and expand the settled volume of the solids without, however, causing any substantial amount of the solids to leave the cracking zone. A mass of solids in this condition may be described as ebullated and the technique of using such a mass to obtain superior contact among liquid, gasiform, and solid materials is described in copending application Serial No. 743,304, filed June 20, 1958. Using the ebullating technique, the desired residence time in the cracking zone may be achieved with a very tall reactor or by using a reactor of moderate height but recycling a substantial amount of liquid through the reactor.

At least part of the elfiuent from the cracking zone is' then passed to a catalytic hydrotreatment using any of various processing techniques, e.g., flowing the cracked oil through a fixed bed of catalyst in an upward or downward direction with the hydrogen-containing gas flowing concurrently with or countercurrently to the oil. A particularly desirable method of carrying out the catalytic hydrotreating or hydrodesulfurization step is to flow the oil and hydrogen-containing gas concurrently upward through a mass of hydrogenation catalyst in the hydrotreatment zone with the velocity of the liquid being high enough to cause the mass of catalyst particles to become ebullated, i.e., to he in random motion without leaving the hydrotreating zone. It is often desirable to employ a recycle stream in the catalytic hydrotreating zone as described in application Serial No. 457,839, filed September 23, 1954, now US. Patent 2,910,433, using a recycle ratio of at least 6 volumes of treated oil to each volume of fresh oil. In addition to the advantages of recycling oil in a catalytic hydrotreating zone as disclosed in the latter application, e.g., washing of the catalyst, temperature and reaction control and avoidance of too high a preheating temperature, if the technique of ebullation is used, the recycle stream provides for the achieving of the relatively high liquid velocities necessary for the mass I of catalyst to become ebullated and at the same time provides for a sufficient residence time of the oil in the catalytic hydrotreating zone without the necessity for a reactor of great height.

The nature of the recycle stream from the catalytic hydrotreating second zone to the cracking first zone may vary considerably depending on the specific process being carried out. For example, if it is desired to maintain the cracking zone at a substantially higher temperature, e.g., 50 F. higher, than that within the catalytic hydr treating zone, the recycle stream from the catalytic hydrotreating zone to the cracking zone should not be. so large that it would have the effect of undesirably lowering the temperature in the cracking. zone. In this case, the recycle stream would not ordinarily be more than 2 volumes for each volume of fresh oil fed to the cracking zone. In addition, liquid may also be separately recycled around the cracking zone. However, if a larger recycle stream is desired, the recycle liquid from the. catalytic hydrotreating zone may be combined with the feed oil prior to the preheating of this oil flowing to the cracking zone. If a temperature difierence between the catalytic hydrotreating and cracking zones is not particularly desirable, it is possible to eliminate a separate recycle stream around the cracking zoneby having only one recycle-stream from the catalytic hydrotreating zone; a portion of this' recycle stream may also be sent back to the hydrotreating zone without again, passing through the cracking zone. Such a single recycle stream has the advantage of minimizing the equipment needed for recycling and thushas the cifect of keeping. the overall equipment cost of the system relatively low;

In general, the recycle stream from the catalytic hydrotreating zone to the crackingzone will be atleast- 0.5 volume for each volume of fresh oil fed to the cracking zone. Although suiiicient beneficial effects of the. recycle stream of this invention are often. obtained when the,- recycle ratio does not exceed 2,:1, it maybe desirahle'in, some cases to use a muchlarger recycle ratio, e.g., when the recycle stream from the catalytic hydrotreating zone to the cracking zone is the only recycle stream in the system and ebullated solids are present in one or both zones. In such case, a large recycle ratio, e;.g-., :1, may be used to maintain the liquid velocity sufficiently high for the ebullation of thesolids.

As disclosed in application Serial No. 737,711, the hydrogen supplied to the catalytic hydrotreatingzone and-, if desired, to the cracking zone, is usually. in the formof a gaseous stream containing otherv constituentsv such as carbon oxides, nitrogen, methane, ethane and steam. Theamount of this gas freshly supplied to, the

1 catalytic hydrotreatingzone is usually adjusted to provide' at least 250' cubic feet (standard'conditions) of hydrogen, and preferably about 1500 to 2000 cubicfeet, per. barrel of charge stock entering the catalytichy drotreating zone. When thisfresh hydrogen is combined with recycled hydrogen, a total of about l000-to 10,000 cubic feet of hydrogen per barrel of charge. stock. enters the catalytic hydrotreating or hydrodesulfurization zone.

The liquid phase cracking stepat elevated pressure is carried out at a temperature in the range of about 700 to l000' F., preferably 750 to 900 F., and in the presence of hydrogen and/or a comminuted'contact material, e.g., clay, bauxite, silica gel, iron' ore or even a spent cracking catalyst. In this liquid phase cracking step, a

7 contact} material having absorptive surfaces'may'be-used but there is no advantage in using such'a material: since its.cataiytic prop'erties are soon lost- The catalytic hydrotreating or hydrodesu'lfurization step may suitably be carried out at temperaturesin the range of about 650 to 850 F., preferably 750 to 830 F., and-pressures in'the range'ofabout 500 to 5000 pounds per square inchv gauge (p.s.i:g.), preferably 1500- to 3000 p.s.i.-g., Anysulfactive hydrogenation catalyst may be employed. in the. hydrotreating zone, e.g. cobalt molybdate supported on- 4 alumina, tungsten sulfide, nickel sulfide, or a mixture of iron and chromium oxides. In this connection, it should be emphasized that the hydrogenation catalyst, which may be any catalyst recognized in the art as catalyzing the hydrogenation of hydrocarbons even in the presence of sulfur compounds, is a material which is substantially different from any comminuted solids that may be present in the cracking zone, according to this invention, either in the form of a slurry or as ebullated solids which remain in the cracking zone. While the latter comminuted material may aid in the precracking step, it is generally .much cheaper than the hydrogenation catalyst and its chemical and physical structure much less critical. Although hydrogen may be present in the cracking zone, the degree ofhydrogenation occurring in that zonewill generally be less than. in the catalytic hydrotreating zone.

The process of this invention is particularly useful when applied to heavy oils havingv a. high. content, iie., 40 parts per million (p.p.m.) or more, of. metallic impurities in the form of oil-soluble, metallo-organic compounds, since it is in the catalytic hydrotreatment of these oils that the problem of; inactivation of the hydrogenation. catalyst due to ash deposits is the most, serious. Broadly, the process of the inventionisparticularly valuable in refining. heavy oils with gravities below about 30 API and especially below 20 API. While such-v heavy oils usually contain at least 10% by volume of hydrocarbons boiling above 900 F., these high-boiling hydrocarbons are'frequently inexcessof 20% by volume of the heavy oilor charge stock. Very heavy oils with gravities of 15 API or lower and containing by.

volume or higher. of hydrocarbons boiling above 900*" F. can be successfully refined by the process of this invention whereas no other known hydrodesulfurization process is operable with such very heavy oils for any. period that could be considered commercially feasible.

To facilitate understanding of the present invention further, reference is now made to the accompanying drawings which represent typical flowsheets embodying;

the two-step process with overall recyclev otv the. invention.

FIGURE 1 shows the introduction of hydrogen-containing gas and clay by lines 10 and 11, respectively, into line12. which supplies the charge stock to preheater 13.- and'thence to cracking coil 14. Prior to entering crack:

ing coil 14, the mixture is further mixed with oilrecycled from the catalytic hydrotreatment zone by way of line 15 and/or 16. The flow of oil inlines 15; and 16. iscon:

trolled by valves 17 and 18, respectively, and dependsonthe degree to whichit; is desiredto reheat the catalytically, hydrotreated oil in heater 13. The-clay is carried in suspension by thetotal oil admixedwithhy drogen: containing gas. The slurry of, clay. andoiltogether with hydrogen-containing gas-passes from. coil"1 4 through, line. 19 into the bottom of reactor 20, containing a mass of sulf-active hydrogenation catalyst particles. The rate, or flow of the liquid phase upwardly through reactor 20 is sufliciently high to suspend the catalyst particles with a random movement but insufficient to carry these. particles ouhot reactor 20, i.e., the catalyst is. ebullated. The oil-clay slurry leaves reactor 20'by way of'line 21 at a level where the liquid phase in reactor 20 is substantially free of the ebullated catalyst particles. A large. portion of, the withdrawn oil-clay slurry is recycled'to cracking coil'14 through line 15' and/or 16 as previously set out. A further portion of the oil from reactor- 20' may, if desired, be recycled to the bottom of reactor 20: by means of'line 22 the flow through which is controlled by valve 23. Pump 24 serves to move slurry through line 21'to whichever of recycle lines 15, 16 and 22 are in use; Theremainder of the slurry leaves the reaction system through line 25 and is then suitably processed to separate the clay therefrom and'to fractionate, the treated oil} as may be desired. The gas phase leavesreactorztl through line 26: A substantial portion ofthe gasiformi effluent from reactor 20, after being cooled to. separate normally liquid hydrocarbons therefrom and then being reheated, is recycled by means of blower 27 and line 28 and/or 29, to the bottom of reactor 20 and/or the inlet of cracking coil 14 depending on whether or not it is desired to have more hydrogen in the cracking zone. The flow of hydrogen through lines 28 and 29 is controlled by valves 30 and 31, respectively. The remainder of the gasiform efiluent of reactor 20 is withdrawn from the reaction system through line 32 and treated to condense and separate vaporized gasoline and other hydrocarbons produced by the process.

FIGURE 2 is a diagrammatic representation of unitary apparatus for carrying out the two-step process of this invention. Cylindrical vessel 40 is divided by perforated plate 41 into lower cracking section 42 and upper catalytic hydrotreating section 43. Hydrogen-containing gas and/or clay from lines 44 and 45, respectively, are mixed with charge stock in line 46. The mixture is sent through preheater 47 and thence to the bottom of cracking section 42. However, before the mixture enters cracking section 42, it is further mixed with a recycle stream from catalytic hydrotreating zone 43 flowing through line 48 and/or 49 depending on whether it is desired to heat further any part of the recycled catalytically hydrotreated oil. The hydrocracked oil and gas rising through section 42 pass through perforated plate 41 into section 43 containing a sulf-active hydrogenation catalyst. It is frequently desirable to have a mass of particulate solids, e.g., alumina or silica, present in lower section 42. to facilitate the liquid-phase hydrocracking of the charged oil. In such case, the particulate mass is preferably maintained in an ebullated state which is easily maintained with the aid of the recycled catalytically hydrotreated stream and, if desired, an additional recycle stream of the hydrocracked oil drawn from the upper part of section 42 through line 50 and injected by pump 51 into the bottom of section 42. While the mass of solids in section 42 is expanded by ebullation, the highest level reached by the randomly moving particles of the ebullated mass is well below the level at which liquid leaves section 42 through line 50 for recycling.

The mixture of liquid and. gas, passing through perforated plate 41 after the heavy oil has been hydrocracked, continues to flow upwardly through section 43 in contact with a mass of sulf-active hydrogenation catalyst. Again, it is preferable to maintain this mass of catalyst in section 43 in an ebullated state and, for this purpose, either the recycle stream from catalytic hydrotreating zone 43 to cracking zone supplied through line 48 and/or 49 is sufficient or an additional portion of this recycle stream may be passed directly through line 54 and distributor 56 into the lower part of zone 43. This recycle stream of oil which has been subjected to catalytic hydrotreatment passes through line 52 and pump 53. A heat exchanger 55 in line 54 may be used to adjust the temperature of the recycle stream of catalytically hydrotreated oil passed directly to zone 43 and, hence, to adjust the temperature in zone 43. The distribution of liquid from pump 53 to lines 48, 49 and 54 is controlled by valves 57, 58 and 59, respectively. The ebullated catalyst particles in section 43 do not rise to the level at which liquid is withdrawn through line 52. Part of the product oil is taken from the treating system by line 60 to a fractionator'for recovering desired hydrocarbon fractions. A gasiform effluent leaves section 43 through line 61; vaporized hydrocarbons and hydrogen are recoverable from this efiluent. The recovered normally liquid hydrocarbons, i.e., those having four or more carbon atoms in the molecule, are part of the total product oil obtained by the process of this invention.

To illustrate the invention still further, a specific ex,- emplary operation of the system shown in FIGURE 1 will now be given.

Boscan crude having a gravity of API, a sulfur content of 5.5% by weight, a Ramsbottom 'carbon'res idue of 15.5% by weight and an ash content of 2400 p.p.m., 90% of the ash being in the form of porphyrim type vanadium compounds, is mixed with 1.1% of clay based on the weight of the crude and charged together with fresh hydrogen to preheater 13 where it was heated to 825 F. The preheated mixture containing 6000 cubic feet (standard conditions) of hydrogen including that recycled by line 29 for each barrel of crude is passed at a pressure of 3000 p.s.i.g. through cracking coil 14 where over 50% by volume of the components boiling over 900 F. are cracked to lower molecular weight compounds and over by weight of the metallic impurities in the form of soluble metallo-organic compounds are removed or insolubilized. Approximately 50% by volume of the crude boils above 900 F. prior to cracking, while on the order of 25% by volume boils above 900 F. subsequent to cracking. The temperature range in the cracking coil is 825 to 850 F. The effiuent including unreacted hydrogen from cracking coil 14 flows to catalytic hydrotreating reactor 20 containing a mass of hydrogenation catalyst particles, cobalt molybdate supported on alumina. Conditions in reactor 20 are a pressure on the order of 3000 p.s.i.g., a temperature of about 775 F., a total liquid flow rate 50 to 60 gallons per minute per square foot of horizontal cross section of the reactor including a recycle ratio of 20:1, and a space velocity based on charged crude of 0.33 barrel per day per pound of catalyst.

Under the foregoing conditions and starting witl freshly prepared catalyst and a sole recycle stream from the top to the bottom of catalytic hydrotreating reactor 20, the process yields a liquid product of satisfactory gravity and sulfur content until the catalyst age reaches 4 barrels of crude per pound of catalyst. At that point, however, the process must be discontinued because the pressure drop across cracking coil 14 becomes prohibitively high due to the formation of solid deposits on the inside of cracking coil 14.

The deposits in cracking coil 14 are removed and the process is started up again using the same conditions as before except that the sole recycle stream used with a recycle ratio of 20:1 is from the top of catalytic hydro treating reactor 20 to the inlet of cracking coil 14. The

process is continued for an additional catalyst age period of 4 barrels of crude per pound of catalyst, i.e., the total catalyst age is then 8 barrels of crude per pound of catalyst. At this point, cracking coil 14 is still substantially free of deposits while the liquid product has a gravity of 24 API and a sulfur content of 2.3% by weight indi cating only a moderate decline in the activity of the catalyst, owing to the additional on-strearn time corresponding to 4 barrels of crude per pound of catalyst. The process can obviously be operated for a substantially longer period of time without the necessity of interrupting it due to the formation of solid deposits or the inactivation of the catalyst.

The preceding comparative periods of operation illustrate the beneficial effect of using a recycle stream from the catalytic hydro-treating zone to the cracking zone in reducing the formation of troublesome deposits therein.

Another specific operation of the process of the invention will be described in relation to the plant shown in FIGURE 2. The use of clay or similar contact material is not involved in this case.

The oil feed to the plant is 10,000 barrels per day of Kuwait residuum, essentially all boiling above 975 F. This feed has a gravity of 83 API, a sulfur content of 5.3% by weight and a soluble vanadium content of 200 p.p.m. The feed is mixed with a gas containing about by volume of hydrogen from line 44. The total amount of hydrogen mixed with the oil is 60,000,000 cubic feet (standard conditions), of which 25 is freshly prepared hydrogen while the remainder is recycle hydrogen from line 61 after appropriate scrubbing has removed hydrocarbons therefrom. The combined hydrogen-feed oil stream then mixes with 15,000 barrels per day of a liquid recycle stream which is obtained by way of -lines'52 and 49 from the top of catalytic hydrotreating "section 43. This total stream then passes through heater 47 wherein-it is heated to 850 F. The'total stream, thus preheated, is then combined with 90,000 barrels per day of liquid recycled from the top of cracking section 42 via line 50 and pump 51. The mixed streams then enter the bottom of section 42.

Cracking section 42 contains a mass of /s inch diameter Alundurn spheres. With liquid flowing upwardly through section 42 at a velocity of 100 gallons per minute per square foot of horizontal cross section, the Alundum mass is expanded about 35% over its settled volume and the individual spheres 'are in a state of random motion. The rate at which the Kuwait residuum is supplied to section 42 corresponds to a space velocity of 2 volumes of residuum per hour per volume of the ebullated mass of Alundum spheres.

Except for the portion of the liquid that is recycled by line 50, the liquid and gases reaching the top of section 42 are uniformly admixed with a liquid stream'recycled by lines 5-2 and 54 and this mixtureis passed upwardly through hydrotreating section 43. The liquid recycle from line 54 amounts to 80,000 barrels per day. The liquid flow up through section 43 is at the rate of 90 gallons per minute per square foot of horizontal cross section suflicient to ebullate a mass of cobalt molybdate catalyst pellets in section 43.

Catalytic section 43 contains 25,000'pounds of A2 inch diameter cobalt molybdate extruded catalyst pellets. The catalyst mass is expanded about 25 due to the ebnllating conditions. Referring to the residuum charged to the plant, the space velocity is 1.5 volumes per hour per volume of the ebullated catalyst mass.

In this operation, the pressure of the system is maintained at 3000 p.s.i.g. The temperature in section 42 is held at 875 F., whereas in section 43 at 790 F. This difference in temperatureswithin a single reactor is essentially obtained by cooler 55 through which the liquid recycle of catalytic section 43 passes.

The importance of the small liquid recycle stream passing from the top of catalytic section 43 to the bottom of section 42 through line 49 is readily demonstrated as follows. If this liquid recycle stream is eliminated from the system, the gravity of the liquid recycle passing through line 50 begins to decrease and ultimately reaches the very low value of 5 API. At this point, carbon is found in relatively large quantities in a sample taken from line 50. If operation is continued at this condition, it becomes necessary Within a few days to shutdown the reactor because of excessive pressure'drop acrossrecycle line caused by plugging due to carbon deposits V which even'interfere. with the operation of pump 51.

However, in accordance with this invention, the use of 15,000 barrels per day of liquid recycle from the top of catalytic section 43 through lines52 and 49 makes the system operable for long periodsof time without difliculties due to carbon deposits. This liquid recycle is of high quality, having a gravity of about 15 API and being highly hydrogenated and desulfurized to a material extent. As a result of the addition of this liquid recycle through line 49, the gravity of the liquid recycle in line 50 is 5 APl as compared with 5 API when the liquid recycle through line 49 is eliminated. Apparently, the dilution by the high quality liquid recyclethrough line 49 makes the system operable for months with essentially no carbon being formed, while yielding high quality liquid products. Thus, charging the 8.3 API gravity Kuwait residuum containing 5.3% by weight of sulfur Over stock and .only 15.5% very heavy oil boiling above 975 F. .Such results reflect operating conditions which ,prevent the catalyst in section 43 from becoming poisoned as a consequenceof the precracking effected in section 42 which, in turn, could not be prolonged without-the liquid recycle through line 49.

As is known in petroleum testing, the determination of hydrocarbons boiling at temperatures above 600 F. is made under reduced pressure. All references herein to hydrocarbons boiling above 600 F. are, therefore, mtended to have been determined under reducedpressure.

Many modifications of the illustrative embodiments of the invention will occur to thoseskilled in the art. For instance in FIGURE 1, the fresh hydrogen of line 10 may be injected directly into the bottom of reactor 20 and recycle. hydrogen from blower 27 may be introduced into line 12. In view of the various modifications of the invention which may be made without departing from the spirit or scope thereof, only such limitations should be imposed as are indicated by the appended claims.

What is claimed is:

l. The process of refining a sulfur-containing heavy oil having at least 10% by volume of hydrocarbons boiling above 900 R, which comprises passing at elevated pressure said heavy oil in the liquid phase and hydrogen through a crackingzone to convert at least 25% by volume of said hydrocarbons boiling above 900 F. to hydrocarbons boiling below 900 F., and contacting at elevated pressure the thus cracked oil in the liquid phase andthydrogen with a particulate sulf-active hydrogenation catalyst in a hydrotreating zone, while recycling refined liquid oil from said hydrotreating zone to said cracking zone at a rate of at least 0.5 volumes of said refined oil for each volume of said heavy oil entering said cracking zone, the liquid flow rate of the thus cracked 'oil .through the hydrotreating zonebeing sufficient to maintain said particulate hydrogenation catalyst in random motion.

2. The process of claim 1 whereina mass of particulate solids. is maintined in said cracking zone in random motion.

3. The process of claim 1 wherein a portion of the cracked oil inthe liquid phase is recycled from the outlet end of said cracking zone to the inlet end thereof, a temperature not exceeding about 1000 F. is maintained in said cracking zone and a lower temperature not exceeding about 850 F. is maintained in said hydrotreating zone.

4. .The process of claim 1 wherein a portionof the cracked .oil inthe liquid phase is recycled from the outlet-end of. said cracking zone-to the inlet end thereof and a portion'of the refined liquid oil is recycled from-the outlet end of said hydrotreatingzone to the inlet end thereof.

5. In a process'of refining. a sulfur-containing heavy oil having at least 10% by volume of hydrocarbons boiling' above 900F. wherein said oil is cracked in the presence of hydrogen while passing in the liquid phase at elevated pressure through a cracking zone to convert-at least 25% by volume of said hydrocarbons boiling above 900 to hydrocarbons boiling below 900 F. and the Ithus 'crackedoil 'is reacted While passing in the liquid phase at elevated pressure through a catalytic hydrotreating: zone with hydrogen in the presence of a particulate sulf-active hydrogenation catalyst, and wherein said particulate catalyst is maintained in said catalytic hydrotreating zone 'in random motion, the improvement which comprises recycling a portion of liquid effluent substantially at efiduent conditions from said catalytic hydrotreating zone to saidcracking zone, the volume ratio of the portion of said recycle being in the range of 0.5 :1 to 2:1 based on the sulfur-containing heavy-oil entering said cracking zone. e t

6. The process .of claim 5 wherein a portion of the liquid etfiuent from said cracking zone is recycled to the inlet of said cracking zone and a portion of the liquid effluent from said catalytic hydrotreating zone is recycled to the inlet of said catalytic hydrotreating zone.

7. The process of claim 5 wherein a portion of the 226471076 Haresnape et July liquid effluent from said cracking zone is recycled to the 5 2,731,394 Adams et Jam inlet of said cracking zone and a mass of particulate 2,801,208 m et a1 July solids is maintained therein in random motion, 2,853,433 f' SePt- 1958 8. The process of claim 5 wherein a temperature not 2,884,371 Knshenbaum 6t P exceeding about 1000 F. is maintained in said cracking zone and a lower temperature not exceeding about 850 1 FOREIGN PATENTS F. is maintained in said catalytic hydrotreating zone. 763,377 Great Britain Dec. 12,

10 References Cited in the file of this patent UNITED STATES PATENTS 

1. THE PROCESS OF REFINING A SULFUR-CONTAINING HEAVY OIL HAVING AT LEAST 10% BY VOLUME OF HYDROCARBONS BOILING ABOVE 900*F., WHICH COMPRISES PASSING AT ELEVATED PRESSURE SAID HEAVY OIL IN THE LIQUID PHASE AND HYDROGEN THROUGH A CRACKING ZONE TO CONVERT AT LEAST 25% BY VOLUME OF SAID HYDROCARBONS BOILING ABOVE 900*F. TO HYDROCARBONS BOILING BELOW 900*F., AND CONTACTING AT ELEVATED PRESSURE THE THUS CRACKED OIL IN THE LIQUID PHASE AND HYDROGEN WITH A PARTICULATE SULF-ACTIVE HYDROGENATION CATALYST IN A HYDROTREATING ZONE, WHILE RECYCLING REFINED LIQUID OIL FROM SAID HYDROTREATING ZONE TO SAID CRACKING ZONE AT A RATE OF AT LEAST 0.5 VOLUMES OF SAID REFINED OIL FOR EACH VOLUME OF SAID HEAVY OIL ENTERING SAID CRACKING ZONE, THE LIQUID FLOW RATE OF THE THUS CRACKED OIL THROUGH THE HYDROTREATING ZONE BEING SUFFICIENT TO MAINTAIN SAID PARTICULATE HYDROGENATION CATALYST IN RANDOM MOTION. 